1. Field of the Invention
The present invention relates to a switching power supply apparatus including a switching device on a primary side of a transformer and an inductor and a rectifier device on a secondary side of the transformer.
2. Description of the Related Art
In an existing switching power supply apparatus, a snubber circuit is connected in parallel with a switching device to suppress the peak of a surge voltage generated at the time of on/off switching of a rectifier device. For example, Japanese Unexamined Patent Application Publication No. 1-202161 discloses an example in which a commutation diode is provided with a snubber circuit.
FIG. 11 is a diagram illustrating an example of a secondary side circuit of a switching power supply apparatus including a snubber circuit, disclosed in Japanese Unexamined Patent Application Publication No. 1-202161. In the example illustrated in FIG. 11, a secondary circuit including a rectifier diode Da, a commutation diode Db, an inductor Lo, and an output capacitor Co is formed on the secondary side of a transformer. An RC snubber circuit formed of a series circuit of a capacitor C and a resistor R is connected between the two ends of the commutation diode Db.
With this configuration, when the commutation diode Db is turned off, surge energy generated between the two ends of the commutation diode Db is consumed by the RC snubber circuit and, hence, the peak value of a surge voltage is suppressed.
In an RC snubber circuit such as the one illustrated in FIG. 11, surge voltage energy is consumed by the resistor R and, hence, loss is naturally generated in the snubber circuit. As a result, provision of the RC snubber circuit causes the efficiency of the switching power supply apparatus to be decreased.
Japanese Unexamined Patent Application Publication No. 1-202161 also discloses an active snubber circuit in which, in order to solve the problem of the snubber circuit described above, without using the resistor R, a transistor is turned on at the timing at which a surge voltage is generated in the rectifier circuit and the surge voltage energy is released after having been stored in the capacitor. However, in such an active snubber circuit, although the surge voltage energy can be regenerated, there is a problem in that the whole circuit configuration becomes complicated and, hence, an area of a substrate occupied by the circuit is increased.